Perception is inherently multisensory. Animals do not live in separate auditory and visual worlds, they experience a rich environment and interact with cues that are combined across the senses. Impairment of audiovisual processing abilities directly impacts human health, as successful combination is crucial for understanding speech, localizing important events in the environment, and guiding attention. In recent years, several putatively unisensory areas have been shown to respond to an alternate sense. Thus, it seems that an understanding of the traditionally defined auditory pathway is not complete without a thorough investigation of non-auditory influences. Recent work (Porter et al., PNAS, 2007) has demonstrated overt visual responses in neurons of the primate inferior colliculus (IC). The IC is a subcortical structure that nearly all ascending auditory information passes through, so visual influences here likely have a large impact on auditory processing. This is the earliest point in the auditory pathway that visual influences have ever been found. What effect do visual responses have on auditory processing in IC? This proposal seeks to shed light on how neural responses to visual and auditory stimuli interact in the primate IC. Specifically, the experiments described herein aim to (1) investigate the distribution of visual responses within the IC, (2) investigate the spatial and (3) temporal sensitivity of visual responses, with a direct comparison to auditory responses. In the third aim temporal properties underlying integration of the senses in the primate IC will be probed for dependence on the content of the stimulus by looking at responses to conspecific vocalizations, which have a natural temporal offset between their auditory and visual components. All of the experiments described will use extracellular recordings from alert monkeys, with a detailed analysis of the activity of single neurons as well as slower changes in the local field potential. PUBLIC HEALTH RELEVANCE: The inferior colliculus is an auditory brain nucleus that has recently emerged as a candidate region for prosthetic devices, due to its surgical accessibility and its location within the auditory pathway. Understanding how the IC integrates visual responses in primates is a critical step in creating a usable prosthetic implant for patients who have damage to the auditory nerve. This proposal will uncover important information to guide the design of these implants, as well as a more general understanding of audiovisual integration which bears on a wide variety of disorders.